Lighter pavement really does cool cities when it’s done right

When heat waves hit, people start looking for anything that might lower the temperature. One solution is right beneath our feet: pavement.

Think about how hot the soles of your shoes can get when you’re walking on dark pavement or asphalt. A hot street isn’t just hot to touch – it also raises the surrounding air temperature.

Research shows that building lighter-colored, more reflective roads has the potential to lower air temperatures by more than 2.5 degrees Fahrenheit (1.4 C) and, in the process, reduce the frequency of heat waves by 41% across U.S. cities. But reflective surfaces have to be used strategically – the wrong placement can actually heat up nearby buildings instead of cooling things down.

As researchers in MIT’s Concrete Sustainability Hub, we have been modeling these surfaces and determining the right balance for lowering the heat and helping cities reduce their greenhouse gas emissions. Here’s how reflective pavement works and what cities need to think about.

Why surfaces heat up

All surfaces, depending on the amount of radiation they absorb or reflect, can affect air temperatures in cities.

In urban areas, about 40% of the land is paved, and that pavement absorbs solar radiation. The absorbed heat in the pavement mass is released gradually, warming the surrounding environment. This can exacerbate urban heat islands and worsen the effects of heat waves. It’s part of the reason cities are regularly a few degrees warmer in summer than nearby rural areas and leafy suburbs.

Reflective materials on pavement can prevent that heat from building up and help counteract climate change by reflecting solar radiation back to the top of the atmosphere. White roofs can have the same effect.

To estimate a pavement’s reflectivity, we use a measure called albedo. Albedo refers to the proportion of light reflected by a surface. The lower a surface’s albedo, the more light it absorbs and, consequentially, the more heat it traps.

Typically, the darker the surface, the lower the albedo. Conventional pavements such as asphalt have a low albedo of around 0.05-0.1, meaning they reflect only 5% to 10% of the light they receive and absorb as much as 95%.

When pavements instead use brighter additives, reflective aggregates, light-reflective surface coatings or lighter paving materials like concrete, they can triple the albedo, sending more radiation back into space.

Though the benefits of reflective pavements can vary across the nation’s 4 million miles of roads, they are, on the whole, immense. An MIT CSHub model estimated that an increase in pavement albedo on all U.S. roads could lower energy use for cooling and reduce greenhouse gas emissions equivalent to 4 million cars driven for one year. And when materials are locally sourced, such as light-colored binders or aggregates, the crushed stone, gravel or other hard materials in concrete, these roads can also save money.

Note: Location matters

But not all paved areas are ideal for cool roads. Within cities, and even within urban neighborhoods, the benefits differ.

When brighter pavements reflect radiation onto buildings – called incident radiation – they can warm nearby buildings in the summer, actually increasing the demand for air conditioning. That’s why attention to location matters.

https://theconversation.com/amp/lighter-pavement-really-does-cool-cities-when-it...

I think there is an American city or major town who have done away with black roads, etc and replaced them with less 'heat generating' roads and the Temps have dropped dramatically.

During the day 'civilisation' cities make heat and during the night - they burn like fires with their excessive lighting.

Planting trees around towns and cities will help lower the temperature of urban areas. Supposedly, the trees have some kind of effect that attracts rainfall to the area.

I think you're hubby is onto something there Lisa.
It's not the first time I've heard of that concept.